towing reality

[TRJeff]

The wife and I are looking at purchasing an RV, this will be a jump up from motorcycle camping. After looking at different sizes and luckily talking to a few gracious owners we have decided to look harder a class B. Planned use will be of course camping but also towing an enclosed trailer with motorcycles inside. Concern is, most advertise 5000lb /500lb limit. Towing at altitude and in the mountains, (west and East) and add in manufacturer add ons such as more batteries, generator and what ever we pack, will this not also affect towing, if so how much? What would be a more realistic weight limit?
Thank you all

[markopolo]

Here's a very useful link to a towing calculator: Travel Trailer Weight Calculator

An imprecise estimate of max tow weight to use as a rough guide would be to subtract GVW from GCWR. That, coincidentally, was close to the calculator results for my van.