Building a Rectangle Trampoline, Ideas?

Well, I have some extra steel tubing sitting in my barn from building a classic truck frame and have no use for it now. Taking it to a scrap yard would be pointless and i'm tied up in this truck too much to even think of starting a new project. I have a crappy little round trampoline that just died recently, no point in welding the rusty frame back together. And it got me thinking that it would be simple to just make a rectangular frame and set her in the ground. Already have a hole dug and reinforcing it is no issue. My question to yal are in regards to the type of "replacement" mat you would choose to buy. I have never owned a rectangular one therefor do not know the best company online to order the highest quality mat from. I do plan on double springing it which leads to extensive strain on the mats perimeter and i weight about 180 and consider myself to bounce pretty hard on them. Any recommendations as to a manufacturer to choose from would be greatly appreciated. Thanks everybody. I'm also planning on doing a write up on the whole process due to me thinking its simple. I know theres always unexpected things that arise so it is to showcase any problems i run into in case somebody else has been wanting to do something similar.

On a separate note, I have enough tubing to make it whatever dimensions i please, (no longer than 18 feet though) any ideas on what would be a good size and surface area would also be clutch! Thanks everybody!