Re: Wood or metal?
look for a robust service box intended for outdoor job site or back of a pickup use. Otherwise it may be constructed with parts (hinges, latches and fasteners) and paint coatings that are not corrosion resistant. Road salts (used both for ice and in liquid form for road dust control) and harsh alkaline dust and road vibration might shorten the box service life or make it look pretty ratty quick. Most of the garage shop type boxes sold at Big Box stores will not hold up for for road use for that reason, including the stainless steel models as they seem to be made with a poor grade of SS.
1991 VW Westy (N8IV) aka Vanna, of Ashland, OR
2012 Sprinter RB SMB PT (ALCES2) aka Moose, chill'n in Anchorage, AK