Tire question again for Voltage 3600

St is higher capacity but Lt are not speed limited like st so even though I go with a lower weight rated tire it should be stronger. Is this right to assume

Correct and a assumption that has been proven ever since the ST tires came out and folks found out the hard way more weight capacity does not equate to best long term reliability.

Also I looked at tirerack and they give comparable tires to the 235/85. I know it depends on room on my th with the wheel wells and between tires but I saw a Lt265/75r16 as a option. Could this be a option?

Not a good option and if you notice wide base tires are not a upgrade option for a trailer for several good reasons.

One is a LT265/75 tires has 8"-8.5" tread width. This adds tremendous stress to the tire/wheel/bearings and suspension parts and especially the spring hangers, as that wide tire is sliding sideways around corners (side scrubbing).
Tires we use on trailers have a narrow tread so they side scrub around corner with the least amount of stress/they have less rolling resistance/less heat build up at speed/etc.

Load carrying wheels width works best when the tires tread width matches. You sure don't want to use a 6"-6.5" 16" trailer wheel on a tire with a 8"-8.5" tread. The tread will be balloned and riding on the center of the tread.

The LT265/75 tire has a 10"-10.5" section width. Now add a inch or so on each side for clearance. I doubt your trailer have that much room in the wheel wells

The advantage of a forum is the experience of the dozens of trailer owners who have 30-40 years and hundreds of thousands of miles pulling trailers and has found out the hard way what tires work best and what tires can be a krap shoot. Make the switch to a 16" LT tire that has been recommended by the masses. You sure won't regret doing so.