Re: Cover your tires
I have really never understood the covering of your trailer tires. The tires on my truck are in the sun just as much as my trailers and I have never seen a car or truck tire covered. Just saying...
that's a good question but I think the answer is that as you use your vehicle, the tire itself is shaded at times as you change direction, you have different parts of the tire top or bottom, and the use keeps the weight spread around. And there's the parking on the grass thing. but the boat trailer question presumes a trailer sitting parked in the same place, seldom used. Like I keep my boat in the water and pull it out maybe 4x a year, so the trailer just sits there year round. So a lot of this discussion wouldn't apply to a trailer that's rolled out weekly.
Seems just leaning a piece of plywood against the tire should suffice; assuming you have fenders, too!
One thing to watch: a spare tire laying horizontally on the trailer. That one needs to be covered!
Given my use: 4x a year, maybe once to an in-town mechanic (<20 miles round trip) and 3X to the ramp <3 miles from the trailer lot, that replacing 4 tires is a big expense every 5 years. Maybe I'll do 2 at a time.