You could go with the old Cantenna approach and use a big resistor 6-8 ohms and wire the resistor into a paint can with mineral oil.
Not related to the WiFi cantenna.
You could also put say 12 100 ohm 5 watt resistors in parallel in the can and end up with 8.3 ohms maybe DC to 50 MHz depending on the resistors.
12 5 Watt resistors in parallel give you a 60 Watt load
12 10 Wall resistors equals 120Watt load etc
Bigger resistors equals more watts as do more resistors in parallel.
These resistors are cheap and can be configured into any ohm load.
You can run these type loads for at least several minutes.
Heathkit made one and other manufactures still sell the same thing. These are 50 ohm loads customarily.
https://www.orcadxcc.org/content/cantenna_va7jw.pdfHams have been using this Homebrew load for at least 80 years for stuff up to one KW or more. I use one.
They solder one end of the resistors to a copper rod or maybe a 12 g wire and connect that to a RF connector. The can itself is the negative. as is the outer RF conductor.
You could use any DC connectors you like .
Customarily, there is a relief valve on top which is just a little hole covered by a stiff rubber flap.
Just don't leave it on for too long, it will heat up. Put it on a pie plate for any possible mineral oil escape. Transformer oil these days is better than mineral oil and is silicone. Good if you can easily procure some. Old transformer oil had PCBs.