SkyGypsy,
Also, if you're traveling along a highway (which can be convenient as you'll likely be loaded to your typical traveling weight), you can stop at a highway truck scale. Often in many states, when the scales are "closed" (meaning they're not currently weighing trucks that travel by), you can still drive across the scales and at least get your axle weights displayed on a readout where you can see it. You won't have a paper receipt for this, but it's FREE (always good!), and easy to do. It won't give you the 4-wheel tare that you're looking for, but it will at least get you close.
For a 4-wheel tare you'd probably need to go to an Escapees or FMCA convention (but sign-up ahead of time--they're busy). Alternatively, you can do a Google search for companies that will do RV weighing. I have noted that these are usually located in areas where there are lots of RVs--like Florida, Texas or SoCal.
Rock Doc
2014 Pleasureway Plateau TS in 2013 Sprinter 3500