I think if you tighten the screws until they make contact and then give them an extra quarter turn or so, you would be ok. Non metal trigger guards at one time were mostly nylon. Whether guards are now plastic is a possibility. But neither would take any kind of shock in colder weather like a metal guard does. I have a anodized ADL in synthetic that would be my 'weather warrior' rifle. I dont know if it is nylon or plastic, but it isnt important to me either. I know it isnt metal and would need special consideration when being bumped or in the cold. And as it ages, it could become more brittle...
Without an inch-pound torque wrench it is only a guess at to how tight you have those screws. In most cases, buying a inch pound torque wrench for such use is too expensive. I dont have an inch pound torque wrench, I use what I noted above. Over tighten a screw that only goes into wood and you could pull the threads.
When it comes down to it, some of those screws on the bottom of your stock can change the accuracy of your rifle. Too loose or too tight, it creates stress and changes the group, sometimes with adverse effects. The right amount of tightening would be where they are when you rifle is most accurate. So take your rifle and enough shells to the range and tinker around with the screws there.
There is no 'one size fits all' when it comes to torque specs for screws on the bottom of the stock. It should be tuned, like a piano. Also, Remington is not the only one that uses non-metal trigger guards. They all do it.
