I own an oil filled electric heater, similar to what you listed, but the 1500w size. I have used it in a residence, garage, and cabin, and it worked well. I thought about using it in a travel trailer and did some research on it on another forum. I like the idea of the steady, consistent, heat that an oil filled electric heater provides, but I never have brought it in a travel trailer, mainly due to the size of the unit.
In a camper, I'm not sure this type of heater would be the best choice for a couple of reasons. First, the 1500w model it is a large heater that takes up considerable storage space. Second, I don't think 500 or 700w size, even with the thermal pack, would be adequate near or below freezing.
I use a small 1500w ceramic heater in in our camper, and two of them in our 25' travel trailer, for those times when we have have electric hookups. They work great, but if it is really cold we still use the furnace to bring it up to a comfortable temp first. They have a 1500 and 700w setting, have a fan, and store easily under the seat in our camper, and in a storage compartment in our trailer. I bought them from Amazon, and I think this is what we have: