How do I keep my lan-to-lan VPN tunnel alive 24x7?

First - I am an experienced IT professional but primarily a "software guy".  I have plenty of exposure to network configuration and equipment but I am not a CISCO certified engineer, nor do I play one on TV and I've never slept at a Holiday Inn Express.  I am familiar with creating and maintaining VPN tunnels in limited circumstances.  That is to say, I understand what I've done in the circumstances where I have been involved in creating and maintaining the tunnel but my knowledge base is limited to only those experiences.  This is my first experience with CISCO products.

I have an ASA 5505 vpn appliance.  It is installed, configured and working OK.  It IS NOT configured using the "Easy VPN" stuff.  It is configured with a l2l tunnel (connected to a CISCO 3000 VPN concentrator on the other end).  My issue is that it appears to shut the tunnel down in periods when there is no activity across the tunnel.  The users on the "other side" of the tunnel cannot re-establish the tunnel once it is down.  I re-establihse it by using the ASDM tool to trace packets from our side to thiers.

It appears that the tunnel will stay established as long as there is activity Ispecifically, activity originating from our side of the tunnel) and, as such, I have put a persitant ping in place from to ping from our side to the other side once per minute.  The tunnel appears to persist under this condition.

Any ideas?  I have attached the ASA 5505's running configuration.  However, I have "redacted" the public IP's for security reasons...  (if it helps  "x.y.z.0" is out public subnet, "t.u.v.0" is our internal prival LAN subnet, "a.b.c" is the universal subnet used on teh tunnel and "j.k.l" is the public subnet on the other side of the tunnel)

: Saved
:
ASA Version 7.2(2)
!
hostname ---------
domain-name -------.com
enable password ------------------ encrypted
names
!
interface Vlan1
 nameif outside
 security-level 0
 ip address x.y.z..213 255.255.255.0
!
interface Vlan2
 nameif inside
 security-level 0
 ip address t.u.v.254 255.255.255.0
!
interface Ethernet0/0
!
interface Ethernet0/1
 switchport access vlan 2
!
interface Ethernet0/2
 switchport access vlan 2
!
interface Ethernet0/3
 shutdown
!
interface Ethernet0/4
 shutdown
!
interface Ethernet0/5
 shutdown
!
interface Ethernet0/6
 shutdown
!
interface Ethernet0/7
 shutdown
!
passwd FmZUfYft9vhrGvu2 encrypted
ftp mode passive
clock timezone EST -5
clock summer-time EDT recurring
dns domain-lookup inside
dns server-group DefaultDNS
 domain-name ecsginc.net
dns server-group ecsginc.com
 name-server t.u.v.1
 domain-name ecsginc.com
same-security-traffic permit inter-interface
same-security-traffic permit intra-interface
access-list outside_vpn extended permit ip host a.b.c.33 host a.b.c.25
access-list inside_access_in extended permit ip any any
access-list outside_access_in extended permit tcp any host x.y.z.213 eq ssh
pager lines 24
logging enable
logging asdm-buffer-size 512
logging buffered debugging
logging asdm debugging
logging facility 23
mtu outside 1500
mtu inside 1500
no failover
monitor-interface outside
monitor-interface inside
icmp unreachable rate-limit 1 burst-size 1
asdm image disk0:/asdm-522.bin
no asdm history enable
arp timeout 14400
global (outside) 1 interface
nat (inside) 0 t.u.v.4 255.255.255.255
static (inside,outside) a.b.c.33 t.u.v.4 netmask 255.255.255.255
access-group outside_access_in in interface outside
route outside 0.0.0.0 0.0.0.0 x.y.z.1 1
route outside a.b.c.25 255.255.255.255 x.y.z.213 1
timeout xlate 3:00:00
timeout conn 1:00:00 half-closed 0:10:00 udp 0:02:00 icmp 0:00:02
timeout sunrpc 0:10:00 h323 0:05:00 h225 1:00:00 mgcp 0:05:00 mgcp-pat 0:05:00
timeout sip 0:30:00 sip_media 0:02:00 sip-invite 0:03:00 sip-disconnect 0:02:00
timeout uauth 0:05:00 absolute
group-policy DfltGrpPolicy attributes
 banner none
 wins-server none
 dns-server none
 dhcp-network-scope none
 vpn-access-hours none
 vpn-simultaneous-logins 3
 vpn-idle-timeout 30
 vpn-session-timeout none
 vpn-filter none
 vpn-tunnel-protocol IPSec l2tp-ipsec
 password-storage disable
 ip-comp disable
 re-xauth disable
 group-lock none
 pfs disable
 ipsec-udp disable
 ipsec-udp-port 10000
 split-tunnel-policy tunnelall
 split-tunnel-network-list none
 default-domain none
 split-dns none
 intercept-dhcp 255.255.255.255 disable
 secure-unit-authentication disable
 user-authentication disable
 user-authentication-idle-timeout 30
 ip-phone-bypass disable
 leap-bypass disable
 nem disable
 backup-servers keep-client-config
 msie-proxy server none
 msie-proxy method no-modify
 msie-proxy except-list none
 msie-proxy local-bypass disable
 nac disable
 nac-sq-period 300
 nac-reval-period 36000
 nac-default-acl none
 address-pools none
 client-firewall none
 client-access-rule none
 webvpn
  functions url-entry
  html-content-filter none
  homepage none
  keep-alive-ignore 4
  http-comp gzip
  filter none
  url-list none
  customization value DfltCustomization
  port-forward none
  port-forward-name value Application Access
  sso-server none
  deny-message value Login was successful, but because certain criteria have not been met or due to some specific group policy, you do not have permission to use any of the VPN features. Contact your IT administrator for more information
  svc none
  svc keep-installer installed
  svc keepalive none
  svc rekey time none
  svc rekey method none
  svc dpd-interval client none
  svc dpd-interval gateway none
  svc compression deflate
username admin password ------------- encrypted privilege 15
http server enable
http 0.0.0.0 0.0.0.0 inside
http 0.0.0.0 0.0.0.0 outside
no snmp-server location
no snmp-server contact
snmp-server enable traps snmp authentication linkup linkdown coldstart
crypto ipsec transform-set ESP-3DES-HMAC esp-3des esp-md5-hmac
crypto map outside_map0 1 match address outside_vpn
crypto map outside_map0 1 set peer j.k.l.189
crypto map outside_map0 1 set transform-set ESP-3DES-HMAC
crypto map outside_map0 1 set reverse-route
crypto map outside_map0 interface outside
crypto isakmp enable outside
crypto isakmp policy 10
 authentication pre-share
 encryption 3des
 hash md5
 group 2
 lifetime 43200
crypto isakmp nat-traversal  20
tunnel-group j.k.l.189 type ipsec-l2l
tunnel-group j.k.l.189 ipsec-attributes
 pre-shared-key *
no tunnel-group-map enable ou
telnet timeout 1440
ssh 0.0.0.0 0.0.0.0 outside
ssh 0.0.0.0 0.0.0.0 inside
ssh timeout 30
console timeout 0

!
class-map inspection_default
!
!
policy-map type inspect dns preset_dns_map
 parameters
  message-length maximum 512
policy-map global_policy
 class inspection_default
  inspect icmp error
!
service-policy global_policy global
smtp-server x.y.z.13
prompt hostname context
no compression svc http-comp
Cryptochecksum:4362f4d3bfbfa98870ba242e44cf148c
: end
asdm image disk0:/asdm-522.bin
no asdm history enable
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