Mine is not a 5er, but ... electricity is electricity regardless of RV type though.
If we run some appliances / air conditioner / etc at the same time, we have also blown breakers too, at the shore power pole and inside the camper.
We have found we cannot run things normally (AC electricity) when we have 2 electric heaters on at the same time. Ours are smaller ceramic type heaters, but both are 1500 watt.
One by itself will run just fine and breakers never pop. Two at the same time will cause something to pop.
In order to get around that, we run a separate extension cord (120 household electric construction-orange colored cord) from the shore power plug to inside the camper and use that for a dedicated line for the second space heater.
I get this extension cord into the camper by using the same hole where the trailer's 30 amp cord comes through. I did a little wiring modification for my 30 amp plug to install a surge protector, so when I did that, I made it available to access that area where all the trailer's extension cord rolls up. I can insert the orange extension cord from the outside and pull it inside this way without having to go through any windows or anything. The access is right at the rear of the camper, so the space heater has a great and safe place to sit and run that is not a fire danger.
Since we started doing this, we've never popped another breaker.
This is something you may consider. If one of your space heaters runs successfully on 1500 watts without popping breakers, run a second (normal) 50 or 100 foot extension cord from the shore power post to the camper as a dedicated separate line.
Now, if your shore power hook-up does not have a second plug for a regular household 15-20 amp plug, then of course, you won't be able to do this.
Good luck! Glad you finally found your problem and it really was an easy fix!
Edit:
We have found we cannot run an electric griddle and an electric skillet at the same time through the camper wiring. Although there is an outside plug on the camper, which is absolutely convenient when using electric cooking devices outside, the trailer just can't handle it when 2 are running at the same time. Breakers always pop.
So, even if using our electric skillet / and / or electric griddle outside, I always run that same orange cord to the picnic table from the shore power cord. I have never been in a campground yet that did not have the additional 15-20 amp receptical at the power pole. And, I can always run both appliance at the same time through this same cord. This is something you may consider ... just run an extension cord from the shore power post to whatever high energy electric device you are using. Inside the camper (if we use the electric skillet or griddle), I pull the orange extension cord on through and plug in the electric griddle with it, never through the camper wiring now. It works for us ... wonderfully!