I've got over 1.2 million miles pulling trailers (same size we rv with) for a living.
Leave the slightly taller tires on the trailers front axle. Reason being rotational braking forces can lift the front axle during hard braking events. Shorter tires on the front axle just magnifies the issue and can result in the shorter tires with flat spots caused by the front brakes locking up.
Using different load range tires/tread patterns on a multi axle trailer will have different traction characteristics which can/may show up on wet pavement during hard braking events.
Suspension blocks on a multi axle trailer are a very bad idea for a host of reasons. In fact Dexter axle.....Rockwell American axle doesn't recommend them nor do they make or sell blocks for that purpose.
My local big rig trailer repair shop said they add suspension blocks up to 1" thick to rv trailers but the owner has to sign their liability waiver.
My current 32' 11200 lb 5th wheel trailer needed a 2" lift so I could use 16" LT E tires. The same shop cut the OEM spring hangers off and added longer 3/8" HRS plate hangers with a couple of holes for height adjustment. I had them use 4" wide plates internally braced and welded to the trailers double stacked frame all the way up. They also checked the suspension for alignment.
The cost was just over 400 bucks with tax....in 2003.