The Glantastic LED RV Puck Light - 197 Lumens - Semi-Recessed - Frosted Plastic Lens - Warm white Item # 328-K-58L34P9 is the 4-1/4" diameter you're needing. This is mounted a little differently as you'll have to screw it into the ceiling instead of using spring mounts. view full answer...
I would love to help but I can't really say exactly what all the Swagman Roamer LT Roof Rack for Pop-Up Campers and Camper Shells part # S80510 fits as it's a universal product nor do I know all the inns and outs of every trailer. That said, you obviously can't mount the rack to glass so you'd need to make sure there is adequate space between the glass and exterior edges to mount the feet which have a footprint of 5" wide x 1" deep. I'd also like to point of that the capacity would likely... view full answer...
Your 145/R12 Load Range E (actually a 145/80-12) tire is meant to be mounted on a 12 x 4 inch rim. The Americana # AM20122 wheel you spoke of would work perfectly with that tire size, as long as the weight of the trailer doesn't exceed the 1250 lb capacity of the wheel.
The valve stem isn't included, I'd recommend part # AM20904 which is good up to 80 psi and is compatible with the .453 inch diameter valve stem hole in the wheel.
I've linked to product videos for the wheel and the valve... view full answer...
The ideal bar spread for your rooftop bike rack is the length that allows you to carry ALL of your accessories. I double checked some bar spread measurements for carrying kayaks. They are similar to the bike rack, so 28" should not be a problem. Swagman does not list a maximum crossbar spread, even on their website. But Yakima's version of this rooftop bike carrier, had a maximum crossbar spread of 38".
The Swagman Roamer LT Roof Rack for Pop-Up Campers and Camper Shells - Steel - 7' Long... view full answer...