I’ve been using a heavy watercolour paper instead of wooden boards recently, makes for an alternative support to paint on… not so bulky or heavy as panels!
Remember not to use a blow torch for fusing though, you don’t want any fires! Heat gun for fusing works great.
I always choose at least a 300lb weight version.
The thickness of watercolor paper is indicated by its weight, measured either in grams per square metre (gsm) or pounds per ream (lb). The standard machine weights are 190 gsm (90 lb), 300 gsm (140 lb), 356 gsm (260 lb), and 638 gsm (300 lb).