I've had no problems popping chests on Core just using Camilla with maxed trickery and some +5 ring, no idea what's this shit about needing a super specialzied trickery dude.
Camellia is Half Elf with +3 (6 after lvl 10) Trickery from her Racial Skill Focus. She is already optimized to be party's lockpicker by Owlcat. Same as Octavia in Kingmaker.
I've never had issues with DC for Trickery skill checks in the main camaign, but +5-15 Skill items are beyond rare in Rogue-like. There, especially if you try to hit above your level with 3 skull islands, I had my Kineticist, for example, who had sky-high DEX, class skill and food buffs, rolling critical failures for the trap disarm way more often than I'd like, on Hard. Would be even worse on Unfair.