so my question is can you run a multi effects pedal like a rp300 into a spider 3 half stack?. in my reading on the fourms its my understanding that this either wont work or there would be ill effects from doing this. but im a noob and not 100 percent sure, i found the half stack i want but i want to make sure that i can run my effects pedal thru it. any info is greatly appreciated
There's no reason why you can't run a multi effects into a spider 3.
It just may not sound as good as other amps that are available.

The spiders aren't known for sounding good and since they have effects built in anyway you might find that you wouldn't need to run the RP300 into it in the first place.

If you haven't bought the spider 3 half stack yet you may end up with a better sound if you save a little longer and go for a better sounding amp then run your RP300 into that instead.
In general, modelling amps (such as the Line 6 Spider) don't take external effects units very well. They already have built-in effects and amp simulations, and they tend to sound better than a pedal or multi-fx unit run in front of it, even with a completely clean setting on the amp.

Also, there are better options than the Line 6 Spider in the same price range. The Spider is one of the worst amps in its class, so I'd advise you to stay away from it.

If you really want to use your RP300 multi-fx unit, you might want to look for a nice tube amp to run it through to get the best out of it.

Tell us your budget, location and music genres you like to play and we can help you find a good amp that suits your needs.
The RP300 would be fine going through the Line6 as long as you run the amp without any of the effects on and the EQ relatively flat. You'd be better off with something else, though.

You'd also be better off getting some actual effects rather than using the RP300, especially if you're concerned about sound. That thing sucks tone out of any amp.