Theres a plastic product that fits in the gap as a closure, it comes in 2m lengths & can be cut down if required- maybe get them to sign an xtra & wack em £££s to purchase & fit
With reguards to the strap its not such a bad idea it saves picking them all up if thd lift goes wrong- i'm not aware of it forming part of the lola regs but technically its classed as a live load & so if being lifted by a crane would need securing & if they wanted to get picky i spose by forklift as well. -i have my crane,banksman,slinger & forklift ticket & whilst not normally doing it with a forklift would allways double sling the chains on a tube lift on a crane,tbh its very easy to get complacent when you want a quick lift,& that i'm afraid is how accidents happen-its about lowering the risk as well as the load, so strap it if thats what they want ,that loss of 5mins it takes to do it could save you a 20k fine,2years imprisonment & someones life