Plug off, hole in lid ,cable through (with grommet if posh) , and then....if you are confident that your brews will always be covering the heater and that it wont be touching the sides or base (or very close to) at any point ,seal with hot glue or foodgrade mastic .You may want to fill the FV with water and have some trial runs before you seal it .Alternatively make sure you have a really tight fit of the cable through the grommet and slide to suit and hold with a springclip . Plug back on .Jobs a (sort of) good 'un . :thumb:
That bit about not touching the base is pretty vital....I had a bad incident with a heater sliding down and melting through the FV when I was away for the weekend ,once .NOT recommended .Houses burned down tend to cause offence and inconvenience .
When using one of these heaters ,also ,be good and sure what the specs are ,whether it needs to be fully immersed at all times and all that .I have some ancient homebrew heaters that came with special 2 hole rubber bungs for DJs but I dont know if they make them these days .They had to be fully submerged and upright so you had to keep an eye on them and reseal them often .
LIke Rob says ,concentrate on the basics and walk before you can etc etc blah .Get confident in your skills and make some mistakes and learn how to deal with them .Theres a wealth of kits out there now ,do a few to get your hand in ,then branch out......
....but I know what you mean...honey beer....mmmmmm (does Homer S drool)