A Run Flat has a stiffer sidewall will give you a bit more peace of mind.
When checking weights, I use a bathroom scale. Set your self up in a nice level spot and about a 16in box or block to get the tongue at the normal towing height.
Roll one tire at a time onto the scale and then set the scale on the block and put the tongue on the scale and add the three together to get your total weight. Then keep positioning your load until you have at least 10% of the total weight on the tongue. as in... 500lb trailer, min 50lb tongue weight. Going over the 10% is ok but DO NOT over load your hitch max tongue weight. If you are getting close to the max then you need to look at lightening the trailer.