I have not heard of anyone else that does this. Major PITA.
I keep my battery on a charger 24/7 on my 2000 2720SL while closed. The battery box is vented, but I'm not sure how effective it is because the box itself is not sealed very well. Atmospheric hydrogen (diatomic, H2) is among the smallest molecules on earth (much smaller than atmosphere oxygen and nitrogen) and thus to seal it, it has to be much better than even air tight. My point is that there likely are no RV-grade battery boxes sold anywhere that are hydrogen-tight. Fortunately, the same goes for the battery compartment, so my theory is that any hydrogen leaks out of the box and out of the compartment into the atmosphere. So far, so good.
If you believe that theory, and your TM has a 3-stage charger built into the converter, the only thing you need to do when you get home is plug the TM into the wall and leave it there 24/7. If your converter does not have 3-stage charging capabilities built-in, you can install one yourself (about $125). Alternatively, or if your TM shells cover the pigtail access hole like mine does, you can do what I did:
- install a low-current (I use 2A) battery charger inside the battery compartment and connect it directly to the battery (with a fuse). Using a low-current charger should help reduce the risk of generating hydrogen.
- drill a hole in the floor of the compartment just inside the door such that it enters the rear bumper.
- run a short piece of tubing through that hole, and run a wire through the tubing (the tubing protects the wire).
- on the end in the battery compartment, put on a single outlet. You will plug the charger into this outlet. On the other end in the bumper compartment, put a plug.
- You can now plug in this charger with the shells down.
Dave