Hi, I'm new to the forum and have been exploring the topics with great interest. I've noticed several posts about maintaining the charge on the engine battery while the rig is in storage but haven't seen any mention of the technique that I've used on my Winnebago for the past 3 years and plan to use on our recently purchased 08 PC 2350 as well.
I store our 03 Winnebago (and our PC) next to my generator shed (home power backup) where I have installed a 30A hook-up. I replaced the converter charger in the Parallax power distribution panel with a Progressive Dynamics 3 stage plus de-sulfate mode unit so that I can leave the coach plugged in 24/7 without cooking the batteries. For my engine battery I use a BatteryMINDer 1510 12 Volt-1.5 Amp Battery Charger/Maintainer/Desulfator with a BatteryMINDer VPP-12 12/24 Volt Vehicle Power Plug.
https://www.amazon.com/gp/product/B00Q3CM2QY/ref=ppx_yo_dt_b_asin_title_o02_s00?ie=UTF8&th=1https://www.amazon.com/gp/product/B001DZNCNS/ref=ppx_yo_dt_b_asin_title_o02_s01?ie=UTF8&psc=1I plug the charger into the 110 volt outlet nearest to the dashboard of the coach. I plug the charge cable connector into the corresponding connector the 12/24V plug, and plug it into one of the dashboard 12v power sockets. On my Winnie (Ford E450), these are hot with the ignition on or off and I assume they are in the PC as well. This has worked great and requires no modifications to the coach and can be installed without even popping the hood. I can't take credit for it though, I saw it on the Born Free Forum (I had a Born Free prior to the Winnie).