Just ordinary blind rivets Les. 5mm drill bit and lazy tongs/rivet gun to attach them. A box of 500 is only about £12. There are more types of rivet than you can shake a stick at though. If the inside of the panel is going to be visible, then the rivet end might be important. Some tear and flare out - leaving a jagged mess on the inside. A blind rivet just forms a ball and doesn't look bad or have sharp edges.
This type splits as the mandrell is pulled and leaves a 4-legged spider on the inside of the metal
http://www.screwfix.com/app/sfd/cat/pro.js...=18223&ts=47587Sometimes the entire centre of this rivet comes out which then leaves a hole right through the panel.
I use aircraft type rivets, which have the end of the mandrell inside the alloy which is cup-shaped rather than a tube, so there is no possibility of it leaking once fixed.
Les.