If you only have limited space in the cavity between outside panel and inside lining panel, this could be for you. One of these gives you 13mm of extra space. If you need even more space, you could even double-up the flange (2) to 26mm. May be an idea to screw the flanges together with countersunk self-tappers (No. 6) to keep them aligned.
13mm Surface Mount Spacer
Also available:
TEV256: 20mm Surface Mount Spacer