Glue three FT -240-52 toroids together using cut paper bag as a spacer.
The layer of fiber will facilitate a good bond that can be separated with a razor if needed.
As a general rule, a single FT-240 can handle a transmitter capable of 200w, a pair is good for 500w, and three will handle 1500w with reasonable headroom.
True power handling will be determined by the impedance mismatch per frequency.
I managed 7 turns (one crossed thru center) using #10 THHN bifilar.
I like to add an additional strand of wire for lashing my solder joints.
This gives a strong “rebar” type mechanical bond in addition to the solder.
#10 Ring terminals are crimped, soldered, and shrink wrapped.
The negative terminal is also heat shrink wrapped.
I use closed cell foam as a pad under the toroids.
I screw down the negative terminal to the SO-239, then I use the long strand to lash the positive terminal to the center of the SO-239.
I flow solder through the lashings to make a solid connection between the two.
Closed cell foam fits snugly over the top of the transformer, and the watertight lid holds it all in place.