Have been frustrated with the whole strap mess.
Our last trip of last year was to Ridgway State Park in western Colorado - about 340 miles/7 hours. Had a blast, but on the way back the crosswinds caused the battery box cover to go bye-bye somewhere along the drive.
Built a really nice, tight fitting replacement out of 1x2 and 1/8" plywood, finished with a nice gloss black finish. Last weekend took a trip to Lincoln, Nebraska (540 miles). Again, in 30MPH crosswinds, the cover departed (this time on the way there).
Never saw or heard the cover depart in either case. In both cases, the strap was still there at one end of the battery box or the other. Realized the single strap holding the cover down over a dual battery installation is not going to work in our situation. The battery box has cutouts at the top of each end for the wiring to go into the box under the cover. I figure the wind is getting under the box cover there, causing the cover end to lift and force the strap to slide off the other end of the cover/box.
So now I'm building the 3rd battery box cover. A makeshift cover I made out of a floor mat for the return trip was bungied with 2 bungies cross-tied to each other and frame survived 35 MPH cross winds on the return.
I thought about a hinged cover, but realized that would make it awkward to get batteries in or out. So the new cover will have 4 screw eyes for the bungies to attach to. Bungies seem to hold tension better and last longer than those polypropolene straps do, anyway (experience with boats). Will send pics when I get done with the mod.
2014 Rockwood A122 with dual size 24 batteries on tongue behind dual propane tanks
2008 Hyundai Entourage (minivan)