You can improvise a double boiler, Just it might not look pretty. I'd probably do it with an induction hot plate, but a butane stove would work as well. Half fill a pot with water. Place a takeout wooden chopstick in (so that it sticks out a bit) and then a metal bowl that is slightly wider than the pot on top. Turn the stove on medium-low. The chopstick is just to create a bit of ventilation so the steam can escape, but voila, you've got your double boiler. Put the chocolate and cream in the upper bowl and watch it melt. Just remember to refill the water periodically. A glass bowl would work as well, just take longer to heat due to thermal mass.