If you can get your coach weighed by wheel position, like RVSEF does with their portable scales, it'll be best. Few coaches are evenly balanced, so it's not a good idea to assume that your wheel position weights are half your axle weight; some will differ by 1000# or more. The safest thing to do until that time is to inflate tires to the max spec... but ride will be harsh. An alternative to the moveable wheel-position scales, is a weigh station which will let you "straddle" the scale so you can get a weight one wheel position at a time. Not all weigh station operators will want to do that; with some, it's impossible because of the way the scale is positioned.