Hi!
Thermometer...? Who needs one! Not I... and have done so for 30 years.
The two most used covering films Oracover and Monokote and the fabrics, Oratex and Solartex demand nearly the same temp. So it is just a matter of slight adjustment on the iron ... No fancy equipement is needed.
Same as with setting and engine. Bye ear! Don't complicate things
Regards!
Jan K
Sweden