I finally got to put some putty in that Oyumaru reusable mold. I used JB Weld two part plastic weld. It is supposed to be used for plumbing. I got it because it was a few dollars cheaper than Milliput as I am on an extremely tight budget.
I started it around 9am this morning and I let it cure for about 13 hours. I should have left it overnight but I was impatient. After 13 hours, it was mostly hard but there were still some slightly soft areas but not too bad. Next time I will know better. My molded ones aren't as nice as I thought they would be but it was my first time trying this. I won't be redoing them so they will stay as is even though they are a bit crappy. If I ever use the reusable molds again, I will still use the JB Weld putty but make sure I make better molds and let the putty cure a lot longer. One thing to note about the JB Weld putty is that it is really stinky so make sure you have good ventilation. It also sticks to your fingers so wearing gloves probably won't be a good idea as it will more than likely stick to the gloves and make a mess. While it made a mess of my hands, it wasn't that hard to wash off though. With some light scrubbing, it washed off fairly easily.
Here it is next to the original. The putty gas tank does have detail but it is hard to see in the photos. Once I prime and paint them the detail might show a little better. Lots of excess putty to trim off.
Original gas tanks shown in place.
Putty gas tanks shown in place.
Even with the bed in place, the gas tanks will be seen so my crappy molded ones will be seen.