Sure wish Alpacka would provide an answer – I have some mods to test and then remove.
The website provides a few hints. The warning comment on duct tape not adhering well enough to use on rafts returned for mods seems to rule that tape out. Is gaffer tape waterproof enough for use? – my biggest concern. Gorilla tape seems to be a possibility – I found it both adhered moderately well and could be removed readily a few minutes later. It too uses a rubber adhesive and may not adhere enough after a bit of immersion, but should be much better than ordinary duct tape and possibly gaffer.