I like to do the simple and least expensive things first so I'm what some would call a "backyard mechanic" you say your stove is working....... while the fridge and furnace are unhooked?...... sounds like they (the furnace and fridge)are shut-off somewhere already! if your not sure just do a small test by temporarily for this test putting a childs balloon over those open fittings and see if they blow up the balloon and if they do then just get the appropriate cap like someone else mentioned in an earlier post and install with a little teflon tape just to be sure and do the bubble test....... if they don't leak then just cover them with something to keep the dirt out.
I am also a "Backyard mechanic" but also hold a licence for Mechanical Engeniering, (Fancy name for a Plumber and done a bit of gas pipeing also.
Even if I knew that these lines had a shut off valve stareing me in the eye if I wasn't going to hook them up to the proper gas valves I would cap with a brass cap cost maybe $1.
Better to be safe then blown up!
I know that in my Boler
the valve, going to the fridge, is a spring type valve and now these are illeagal to even install on gas lines, in homes, let alone a trailer, vibrated going down a road.
Gerry the canoebuilder