I can add a few things as a newbee owner of a 87
Bigfoot 5er...
My trailer was in tip top condition and I paid $7,500 in December. I had to drive from Texas to Oregon to get it, but the price was right. Not only was it in excellent condition, but it's a
Bigfoot, which is a premium brand. It's a foot wider and longer than a Scamp 19 and therefore more spacious. It also has more frontal area and takes more gas to pull.
I've seen other 5ers listed for what I considered to be low prices, especially compared to pull behinds. My conclusion is that more people want pull behinds because they can use more types of tow vehicles. If a buyer doesn't own a truck or doesn't want to buy one, they won't consider a 5er.
Having said all this, I think you could make a case for either price. If you have to replace the floor, that's a BIG project. (My BF has a molded fiberglass floor.)
No one mentioned appliances, which can be very costly to replace. Mine work great except for the oven. (Burners are fine, only the oven is bad.)
I love my BF! A 5er is the best configuration for my wife and I. It tows easily, is very stable, and is space efficient. But since the TV must be a truck, you can't store as much stuff in the TV.
With twins in car seats, your carrying capacity is even more constrained.
But they can sleep in the "loft" while you and your wife stay up later and get up earlier. A pull behind doesn't have this natural segregation of space.
One thing often omitted in purchase decisions are all the extras: hitch, drain hose, water hose, chocks, etc. The list goes on and on. This adds up fast.
You can make this trailer exactly what you want it to be. Just watch out for the total loaded
weight. For everything you change, consider how it changes the
weight. If you build heavy cabinets, you can't just take them off.
So much to think about.
Sounds like a fun project!