which tires

I'll be going Hankook LT, but there are many other brands available in either of those sizes. Whatever brand you use go with a light truck (LT) tyre. Don't need an aggressive tread pattern.

Cheers
Pop

Tyres, tyres,tyres in Australia

Hi Tessa,
may be worth ringing the manufacturer and asking what the ratings for your tyres are suppose to be. I cannot recall exactly the formula but each tyre must be rated to handle a certain load and I think should also be speed rated although not certain on last bit. I know they checked my caravan's tyres out when I had it registered.
Best of luck with it,
Rgds
Nev

Round black ones

My boat trailer is a similar weight and tandem setup. We went for Federal Ecovan tyres in 215 70 15.
They are a commercial rated tyre for delivery vans etc. The boat gets dragged between Brisbane and Coffs harbour regularly and I am supremely impressed by these tyres on the road.
Possibly the most boring looking tyre ever made, but do the business very well. I'll be looking for these again when our other plant trailers need rubber.