I wouldn't count on that to keep them from freezing. For options maybe try Googling "overwintering" with name of each plant after, one by one.

I don't think the picnic table is a good idea. There won't be enough air circulating and you will get mould. I overwinter plants in a smallish greenhouse, but I have a fan going 24/7 and the air stays sweet. If it is going to be below freezing I can put the electric heater on. I think air movement is crucial to keeping plants from rotting off, especially in cold weather. But, I still lose some.

Since these are all tuberous summer bulbs that produce growth in response to warm soils, you are already ahead of the game by growing them in containers! Container soils warm up far faster than inground soils.

I would not risk the bulbs by keeping them outside - even in a "mild" winter, that's pushing the envelop a bit. Store them in a cool basement, garage or shed. As soon as the evening temperatures start warming up in spring and below freezing nights rare (mid to late March?), bring them back outside and locate where they will receive plenty of sun and any reflected heat.

I did this with both dahlias and cannas for years and the containered plants always started producing new growth very early and were weeks ahead of any inground planted equivalents.