I`ve fitted one and was surprised at how easy and how well it went,used a 2 1/4 mechanical flange and then the element screwed into this. 64mm hole saw,this meant the male part of the flange which goes from inside to out actually screwed through the hole (very tight fit) seemingly cutting its own thread as it went and then the female bit tightened up rock solid with a spanner without turning the female inner as well,used no gaskets and no sealant,just ptfe tape on the threads and same when screwing the element into the flange. Got everything as tight as possible by hand first and watch out my thumb turning on the thread split the skin nicely,tea break to stop the bleeding. No leaks,heated to 50 C in just over a couple of hours(only 250litre),got my element about 8-9 inches from the bottom(11 inch element),below it,it is still well cold so as my water pick up is from the bottom of the tank and the water input at the top i just looped the reel back to tank,put on the pump for 20 mins with the element still on and then hosereel,tank all seemed a fairly even temp after this time at about 47C and at this temp its uncomfortable to keep your hand submerged. Finished messing at 8.30 pm last night(element switched off) and the water was still warm at 41C going to bed gone midnight,it hadn`t cooled fully at 9am (it was inside but not in a heated room). When i say hadn`t cooled fully i mean it wasn`t very warm but neither was it cold.
Just thought i probably got a false reading at 41C at gone midnight as i took the reading from the top,average temp if i had mixed the water would have been less i guess.