Typical electrical usage

Looks like you will have other issues through the coming years with this mother in law to be!! I would not let the sun set until I had purchased a meter as suggested in this forum. I had no idea they were available or were that cheap. If you are powering the 5th wheel with a cord plugged into a standard outlet then this meter could be plugged in at the outlet and every drop of watts would be recorded. The local power company publishes their rates and you could do the math. This would put her in her place rather quickly and permanently. I don't like issues to fester and meet them head on. But however on a positive note, if you and this guy spend your lives together you can at least have a hand in picking her nursing home someday.