While I have my Camper insured itself, I use my home contents policy and insure my camping contents thru that. The 2 x engels and Honda generator are listed items and that costs approx $25/item per year for full cover. For smaller items like bikes, kayaks, camp tables, chairs etc... I have unspecified contents of $3,000, of which no single item can be over $600 in value. From memory this is around $60/year (could be wrong on that figure). Excess is about $200 on each claim ie. in the one theft, only $200 excess total, not for each item.
Anyway, this was the best and cheapest way I could get cover and apparently is all covered if inside a tent or locked up outside. Worth giving your home insurance company a call and seeing what they offer - mine is SGIO.
Cheers
Captain