No touchy-touchy?
 

The only way I can fit the two heaters together in the sump submersed is on either side of, and touching, my acrylic skimmer. Is this going to be a problem? (2x 300w heaters in a 120g with a 33g sump)

Absolutely not. Do not allow any part of a heater to make direct contact with acrylic. It's bad...I tested it. If you use heaters in an acrylic sump ensure that they have spacers all around so that they cannot make direct contact.

Mind you...my heaters are 500W..so maybe smaller ones can do the damage mine can (and did).

depends on the heaters religion.:lol:

Can I put them in the overflows then?

heaters
 

yes heater in overflow is best.
when your doing clean up in he sump, you will not hit them.

I recently had a heater in a rubbermaid bucket when mixing new water and could smell something funny. Couldn't figure it out to start, kind of smelt like melting plastic. I was lucky enough to catch it before it melted right through. I like the idea of a heater in the overflow.

Good, thank you!