Welcome to the forum.
Re: the Onan Generator not starting - that happens often to Onan gens that sit unused for a while. The carb gets gunked up. Sometimes it can be cleaned and sometimes they have to replace the carb. I had a Onan 4000 that sat unused for a year or so on a dealer lot. It wouldn't start but the dealer cleaned the carb and it worked fine after that. You could try spraying carb cleaner in it but you might have to get it serviced.
Re: Dometic 3 way fridge is not cooling - does it not cool on battery, LP gas or when on electricity? I'd check 12v fuses and 110v breakers first. Light the stove to confirm gas flow. If you smell ammonia then the cooling unit is leaking. The cooling unit can be replaced but you'd want to check the price of new fridge first for comparison.
These guys from New Brunswick sell cooling units: http://stores.ebay.ca/ARCTIC-COLD-RV-RE ... 4340.l2563
it will give you an idea of what it costs.