Thats the go, I would go for an LR for each tyre then of about 70% of your GTM ........ we can get technical though as the max LR of a tyre is achieved at max psi, but thats another can of worms.....but 70% should mean that your tyres are rated to over 40% of the wheel load any more would be a bit academic as the LR for just 2 rims would only be about 1.2t each, higher LR rims are available and costly, go for a mine rated rim though.
When I replaced the suspension on my 14.44 I found the original rims were 1t each for a van of 1850kg with original tyres that were underated, replaced with 15" steel RoH's, rated at 1140kgs I think, a bargain 2nd hand, tyres were upped in LR and to 225's I think, gave a better ride all round and if I whacked a good hole I didn't have to worry about a dodgy Indonesian alloy rim folding up on me. Shop around the less aggressive tread the better and buy on special, a good deal will get you a tyre at under $200 each.