Mr. Rawles:
Hello again from England. The blog is going from strength to strength, keep it up!
With regard to the door hardening, I’d suggest a thick layer of ballistic nylon contained in a quilt as defence against chainsaw or reciprocating saw attack. Ballistic nylon is a lot cheaper than Kevlar and works in a similar manner to the laths mentioned in the article, i.e it clogs up chain and reciprocating blades. It would quite possibly foul up a drill attack also, but I have yet to verify this… It would not, of course, stop a projectile attack.
Ballistic nylon is also very light in weight, but is extremely flammable and gives off toxic gas when burned. For this reason I would suggest making the cover out of a fire resistant material.
The material should be sewn into sections, preferably so they hang horizontally, to prevent settlement, and the finished article would need to be sandwiched to the door between the panel and a light (ply?) sheet, again to prevent fouling and to protect the quilt from fire and other damage.
The weight of up and over doors is critical to the mechanism, the springs etc can get overloaded very easily; I had one shear off the mount and go through a sunroof recently. An expensive experiment!
I cannot suggest any suppliers, being on the wrong side of the pond! but am sure other readers will be able to help out there if need be. Very best wishes to all. – Michael in Worcestershire.