I place a vial on the stove top at medium heat. I closely monitor it by checking the how much the oil rises. Heat expands liquids which increases the pressure in the vial. I've seen vials explode before and that isn't a fun experience. I pick the vial up periodically to0 swirl the contents. I turn the vial over and do the same. The rubber stoppers are more durable than you think. It is designed to withstand heat and corrosive solvents. It will not deteriorate.

I just put the vial in hot water for a few mins. Just dont have the levels go over the seal

Put the vial in a glass with hot water for few minutes and shake it after that. If the crystal are not dissolved yet, repeat the operation.

Stick a needle in it to vent. ( no barrell )
Take a blow dryer, warm it up while swirling it...

Sounds like you are using a Bunsen Burner bud?? Lol

If you heat the bottle in boiling water then physics will take over and the entire bottle will heat up. Swirl not shake and it doesnt matter where the cystals are it will disolve. I place my vials in small pot with water and put burner on till bubbling. Take out, swirl, put back in, repeat until its all disolved. Then at end ill place back in boiling water for a good 35-40sec to guarantee when bottle cools down it wont recrash. Some people vent the bottle but i repeatedly take out and swirl so it doesnt overheat to the point to build that much pressure.