Survival in Single-Dungeon Campaign

[Greysect]

I am a DM, and after my players' latest adventure is resolved, I will be starting a new campaign that takes place in a single dungeon, beginning as they enter it, ending when they escape. The players will be unable to return to towns to refresh and must either create makeshift safe havens they must defend or fight over shelters established by creatures in the dungeon. Gold is useless, as there are little to no vendors in the dungeon. All items must be fought for.

In this scenario, how would one handle skills like Craft(Alchemy) and (Poisonmaking)? The PHB states that gold must be spent on reagents to create these items, but there are no stores. One solution I thought of was to hide sources for material components throughout the dungeon. Do you see any problems with this approach, know of any rules I should take into consideration, or have any comments or suggestions?

[Radar]

I would say, that Survival and appropriate Craft checks would be in place (PCs searching the enviroment for suitable reagents) - Survival for finding, Craft for knowing what to look for and thinking up substitutes for reagents unavailable underground. It wouldn't have to be one person with both the skills - the Craft person could simply explain, what is needed and the Survival person would search for it or say, it's impossible to find around theese parts.