Planter Boxes and Glasshouses

I’m having to shift my vege planter box, have you got any tips for repositioning it, and what I can do to boost the soil please?

I have a large planter box that has no soil, but only bags of mix/mulch. What specific nutrients do I need to add to the mix/mulch to keep it at its best? My vegetables didn't have a good crop this summer. 

How often should I water and fertilise my vegetables (tomatoes, lettuce etc) which are in a planter box? Also, what’s the best way to deter the cats from using my planter boxes as their toilet?

Why have tomatoes in my polycarbonate glasshouse gone mouldy? The leaves are spotted with mould and turn yellow, and many of the flowers don’t develop into fruit, while my outside tomatoes have done really well. 

I’ve been given a glasshouse and wonder what grows well in the glasshouse and what doesn’t. My tomatoes are doing great but the lettuces and spinach are not. Also wondering about a mushroom farm; are they good in a glasshouse?

I have three large, macrocarpa planter boxes in which I will hopefully produce fantastic vegetables. My problem is finding the best product to seal the insides of the boxes, having received a lot of conflicting information. Any advice?