A few may tell you that you can tow with a dodge mini van. Many will tell you to forget it. You can do a search on the web about Dodge/Chrysler/Plymouth mini van transmissions. Here are a couple sites with eye opening reading: What Chrysler Doesn't want you to know.
, and consumeraffairs.com
You must mean that you replaced the front drive axels. Those can fail and/or wear out if the rubber boots get torn and the joint gets contaminated. I don't think that just pulling a trailer will wear them out. There is not much wear if the boots remain sealed.
Pulling a boat is not comparable to pulling a travel trailer. Most of the resistance when moving is from the frontal area of the trailer. A boat has little frontal area and allows the air to flow around it. The travel trailer is like pulling a wall behind you.
It is very easy to overheat the mini van transmission. You can do it easily without overheating the engine. If the transmission starts "hunting" (down shifting and then up shifting repeatedly) it will be getting hot. If you try to run a speed just under the speed it hunts at, it will get hot. Heat kills transmissions.
I have had several caravans. I now refer to the transmission as a slushamatic. Dodge had to detune the transmission to reduce the amount of torgue generated internally.
Beyond the above info, you need to figure out how much the candles you want to carry weigh. That needs to be figured into the GVWR you will need the vehicle to be capable of handling. Each manufacturer establishes several "limits" for each of it's vehicles. Here is an excellant post about the info on another RV forum Manufacturer rating definitions