Well its an interesting idea George... though you might want to look at the weight of that by the time you're finished compared with other materials. Taking aluminium as 1, mdf is 2 and Perspex 2.5 in rigidity ratio for a square section beam, the weights are 1, 1.5, 2.8 in ratio, i.e. to replace a 10mm sq ali bar in perspex you'd need one 25mm sq and it would weigh nearly 3 times more...

How will it work in practice? No idea, never used plastics that way.