138 lbs body weight (63 kg) ?

You are a light fellow.

I'm more heavy myself but I think 70-75 kg persons can right the F16's with alu masts.

In your case about 5 gallons of water (19 kg) should do it for sure, total 82 kg. I'm guessing that about 3-4 will be sufficient though.

Probably best you can do is get a pully setup and a specilized bag that is easy to fill to the required amount. I refer to other for this as I never needed it. I'm about 85 kg.

Wouter