For the first time in my independent adult life, I live somewhere where I expect to be gettign trick-or-treaters!!

I'm pretty excited about this.
So... although I'm normally against dressing up dogs, I think I'm going to make an exception and put Huxley in a costume this year. But I didn't see any mastiff-sized costumes at Petsmart.
Where do they sell mastiff-sized costumes?? If online, which sites do you recommend?
Or are there easy ones I can make myself, armed with some fabric glue?
And most importantly.... I need ideas!!
Right now, I'm envisioning Huxley as a ginormous pumpkin... but I would love to have input from others who have dressed up their mastiffs and hear what worked/didn't work.