YES..... I added 2 more batteries to my Lance 881.
I put them in the area under the drivers side "wing" door. They fit just above the pull valves and plumbing fittings. There are two large wires "battery wires" going to the generator just accross from this area on the passenger side. They go directly to the othermain battery. I tied into them and connected them to the newly installed batteries.
The set up works great and I can go quite a long time on the 3 battery set up. I can watch tv and direct tv with lights on for several hours and still run my cpap and a fan all night with no worries.
No regrets.
$100 in heavy guage wire red and black and splice material and shrink wrapping
$100/ battery for 2 group 31 batteries