The tumbler is for cleaning only. the trimmer is what you get the length of brass back to. when you shot and resize the case will get longer and you need to trim it back or it will not chamber. I would get the abc's reloading book before you buy anything and it will give you a much better idea of what to buy and what to skimp on.
I have never used the type of press you are talking about but I would steer clear of it and get the bench mounted one instead. I have seen lot's of guys build folding benches that they mount them to and actually take them to the range with them so it still might work even living in a trailer.
Mike
