The closest matching trailer interior light to the dimensions you listed of 18 inch by 6 inch would be the # ILL08COB which measures 18-1/4" long x 5-3/4" wide and is LED. Sounds like you may have fluorescent currently which LED will draw less power and be brighter. view full answer...
Yes, the Gustafson RV Sidewall Light # 277-000254 that you referenced could be installed upside down if needed. The shade of the light would not fall out if it was upside down. Since this is designed for an RV application the shade is secured so that it would not fall out due to bumps on the road. view full answer...
I recommend taking a look at the Ultra-Fab Power Twin II Electric Stabilizer # UF39-941705. This is going to give your customers a very good system that has dual 12V motors which function independent of one another to achieve proper leveling and support. The Ultra-Fab will fit so long as the frame of their Santara is between 48" and 80", offers 6,000 lbs of support and large footplates for optimal traction.
I've added a link to a video review of this stabilizer for you to take a look at. view full answer...