Translation:We didn't travel much last summer.
In negative statements (or questions), I would say "much" is possibly marginally better (and it's certainly better in formal use). In positive statements, I would never use "much" in normal conversation, as it sounds a bit odd, although technically it's not wrong. Maybe native speakers from other countries have different views though.
Am I missing something or is the past simple tense same with the present tense for 3rd person plural?