How I sikaflex skins on to steel frames. It's fast and easy, and the stuff is astounding in it's holding power. In this example I lucked out and found some 1/4" thick honeycomb sheet that I'm using to cover the sides of my bluebird with it's roof raised. Everything's the same for sheet skins except this honeycomb material is not as simple to clamp while drying, since it's thicker than sheet material. For sheet aluminum or stainless over steel structure, I simply use a bunch of big supermagnets to hold things together while curing. I use little plastic spacers that were supposed to be for transistors... almost anything between 1/16 and 1/8" thick will do as long as it's plastic. Nice thing is, the sheets don't touch the steel anywhere so there's no chance of galvanic corrosion later. And best of all, NO SCREWS I'm skinning this 5x5 foot door in two sections to better utilize the honeycomb material I have on hand. The following photos are for the top half... I'll do the bottom piece tomorrow after this one is dry.
Sorry, I didn't take photos of the sika bead going on or a photo when I was done beading it, because the day was hot and I had to move quickly. No time for a photo there....All you do is lay down a nice 1/4 - to - 3/8" diameter bead of the stuff so when you bond the two together it squishes out into a nice 1/16-to-1/8" ribbon between the pieces.

For the best bond, it's recommended to sand down to bare metal, and then wipe clean with a rag soaked in pure isopropyl alcohol to remove any possible oil or grease, then apply the primer.

(69K) 600 x 450	Here's the bus almost intact, before I cut out the wheelchair door to make it bigger. Front passenger door is still there, etc	(60K) 600 x 450	Roof is raised, now I'm taking the front stairway and door out. I'm going to cut the new door in and use the material I removed to fill in where the old door was.
(65K) 600 x 450	Front is now door gone, new dooris cut, some of the siding is now bonded on with Sikaflex rear door framed in	(51K) 600 x 676	Getting rear door panel positioned and ready for bonding
(40K) 450 x 600	With a sharpie I draw lines where the glue will go and add tick marks for lineup	(33K) 600 x 408	Here's the panel, marked where to lightly sand, in preparation for the sikaflex primer. I like to prime over fresh bare metal for a great bond
(35K) 600 x 379	My favorite grinder from Home Depot. Get the 4-1/2" Ryobi for 40 bucks, takes all the 5/8"x11 wheels and grinding discs, but it isn't nearly as noisy as the big Milwaukee	(41K) 600 x 436	Glue lines sanded
(64K) 600 x 500	sanding the frame	(38K) 600 x 506	Painting on the primer. If you're old enough the smell will bring back childhood memories of model making glue
(58K) 600 x 402	frame primed and ready to bond	(43K) 600 x 258	primer closeup. you can let the primer sit indefinitely as long as it remains clean. It dries in moments but at least ten minutes is a good rule of thumb
(38K) 600 x 450	Little plastic transistor spacers from ebay	(27K) 300 x 189	I stick a dab of Sika on my (dirty!) finger to pick up a spacer, and plop one every 6" onto the bead of sika
(37K) 600 x 495	Sticking a spacer into the bead. As soon as the bead of Sika is laid, you should work quickly to avoid premature drying. I lay the bead, place the spacers and plop the sheet on as soon as I can	(54K) 600 x 404	Plop it goes, then lightly C clamped for the night. When I'm doing sheet aluminum or stainless, I simply use big supermagnets to hold the sheet on and keep it clamped. It's a good idea to put the clamps or magnets directly over a spacer, to maintain proper spacing between bonded pieces. I usually measure and mark where the spacers will go so later I'll know where to stick the clamps or magnets...