I've never had a problem with the batteries, but I can see how it's possible. Fellow campers in most campgrounds around the country are quite considerate of other campers, so I don't think your problem would be there. The most popular place for theft is at storage facilities. Whenever I store a unit in one of those, I remove the battery entirely and take it home (if it's cold) or keep it locked in a storage bay (it it's warmer). I also remove other things like the clips on the WD brackets, spare tire (if it's mounted and visible), any valuables, etc.
As for securing them for travel and camping, I just use the straps supplied with the battery case. It doesn't seem like much, but I've never had a problem with the battery falling off, or the cover blowing off.
2007 T-286SR Cherry/Granola, #6236, original owner, current mileage: 9473.8 (as of 6/18/21)
1997 T-2653 Blue Denim, #5471
1979 12 1/2' MC, Beige & Avocado, #4639
Past Sunlines: '97 T-2653 #5089, '94 T-2251, '86 T-1550, '94 T-2363, '98 T-270SR