I have been building electric models from coroplast for years. I'm mostly using foam now, for disposable planes, but I started with coro. Most have been small, under 150W, park fliers but some have been larger. You really don't have to upsize the standard electric package. A 24g motor, 8x4 prop, small 3S LiPo and some 9g servos will take you far.

I also like the cheap Suppo 2208/08 motor for a light, speedy setup.
For comparison, I use the following info when doing weight estimates; 2mm Coroplast: 1.462 oz/ft^2 and 4mm Coroplast : 2.306 oz/ft^2. That info is from an old page on the SPAD Underground from the UK. I think it's a little higher than actual, but it makes an estimate safe so I've never back checked it.
Like many types of models, the weight is really dependent on your build techniques. I'm building a new 60" span trainer for my son this spring. I built it with a .46 nitro engine last time but I'll use a 3548 that I have in stock. It works great on 3S and an 11x5.5.
Good luck with your building. I hope you'll give coro a chance.
