Just about every TT will have a battery located by the propane tank, and in a plastic housing with a cover. My 16XRB is by the propane tank.
You can buy a battery case with cover at Wally mart, or any large automotive parts store. Be sure to get one with a cover and strap (to hold the cover on), and mounting the case to the TT's front frame is easy; a couple of stainless steel screws and a drill would do the job.
2015 Jayco Jay Featherlight SLX16XRB (TT)
2007 Ford F150 Tow Vehicle (TV)