This is my robust but cheap heat sealing tool setup:
1. bulk 40W soldering iron (“absolutely too hot”, cost 8 eur)
2. light bulb dimmer 0-100% (cost 7 eur)
3. tool tip from copper tube (quite heavy tip for more stable tip temperature)
4. spare soldering iron tips for different shape sealing tips (3 eur, not needed)
Here in Finland the dimmer can bought for example from here:
http://www.biltema.fi/fi/Rakentaminen/Sahko/Ajastimet/Himmennin-2000022447/
Note: do not use dimmer with any “active” electrical equipment. Plain resistive load like filament light bulb or bulk soldering iron are fine.
The dimmer adjusts the power of the iron. That is not exacatly constant temperature device but seems “enough constant”. If power is adjusted it takes some time to stabilze.
For my next packraft I may buy basic solder station wich has active constant temperature control itself. (Exactly I have high quality solder station already but it is for SMD electronic work and I didn’t wan’t to modify that for packraft making… :D)