Having used the 3 different Markins heads as far back as 2004, my advice is to get the rubber strap wrench. Any auto parts store, Sears, etc., will have them, often sold as "rubber automotive oil filter wrenches". If you ask an auto parts store for a strap wrench they may not recognize it as such (from experience). They usually come in pairs, the thinner wrench band is the one you want to use for a Markins.
The Markins pan bases will likely NOT lock absolutely, such that they will get tight enough by hand turning them. And they may be damaged, as Jrp suggests. Use a strap wrench or something similar like some sort of heavy duty rubber band.
I would be very leery about using Loctite. Think about it- if it is difficult to hand tighten the head enough to keep it locked in place, how are you going to remove it with well cured Loctite? A strap wrench, used properly, will hopefully do that job (but never tried). But it is best to use the strap wrench to install it without Loctite.
Edit: I frequently swap heads. My experience is that a head, properly seated when installed, tends to tighten with time, not loosen. Sometimes severely. Even with a strap wrench, used properly, it can be a challenging operation to remove it. My sense is that Loctite can only make that more challenging, to say the least, which is why I strongly recommend avoiding any thread locker on the ball head stem bolt.