It it's a typical swinging door you can go to your local hardware store and buy a "rubber door wedge / doorstop" (couple dollars) Usually about 4 inches long by 1 inch high and you wedge it under the door.
Or use a bungie cord. Or your husbands belt. Or an old pair of nylons. Or a shoestring or two tied together. Or a chair. Lot's of things as you can see.
IF, on the otherhand it's a "sliding" door:
You can purchase from your favorite hardware store a metal "extendable / adjustable" closet rod. Make sure that it is from 24 to 36 inches.
Basically all it is is a tube inside a tube that when screwed together are expandable up to 36 inches or retracted to 24 inches. Simply adjust to the length and place on the bottom track thus preventing the door from closing. Cost is under $10. """"NOTE***** The aformentioned "rubber door stop" will work here just as well.
A Bad Day At Sea [with power] Always Beats A Good Day At Work
Alaska 2014 - haven't picked a cruise yet
Carnival: Glory 2004, Destiny 2008, Splendor 2009, Freedom 2011, Valor 2012
Celebrity: Summit 2011
Princess: Ruby 2010, Caribbean 2013